Computed tomography technique for the measurement of bone defects adjacent to uncemented acetabular components of total hip replacement: development, validation and clinical application.

Abstract

This thesis describes work, the aim of which was to develop a computed tomography (CT) technique that provides accurate and reliable volumetric measurement of bone defects adjacent to uncemented metal-backed acetabular components of total hip replacement (THR). Periprosthetic osteolysis (PO) around THR is a major clinical problem in the mid-to long term post-operative period. Some implants remain well fixed in the presence of significant bone loss, and the hips may also be asymptomatic. However, undetected, the PO can lead to dramatic implant failure, or periprosthetic fracture, requiring complex and expensive revision surgery, with associated morbidity. Clinical assessment of THR for PO has relied on plain radiographs. However, numerous studies have shown that there are major limitations of this method in detecting the presence and extent of osteolysis and the volume of the defects cannot be quantified. Therefore, clinical management decisions regarding the need to revise prostheses for PO have been based on this unreliable diagnostic tool. Until recently, the use of CT to detect and measure defects was not effective because of the resulting artifact from the metallic components of the THR prostheses. The studies described in this thesis represent the development, validation and the clinical application of a CT technique for quantification of acetabular periprosthetic osteolysis after THR. In the first in-vitro validation study, a CT protocol was developed using a conventional CT scanner with limited CT scale (up to 4,000 Hounsfield units [HU]). The CT operating conditions were determined that enabled volumetric measurements that were accurate to within 96% for small and large defects and precise to greater than 98% for small and large defects. Since the ilium is the most commonly affected site by PO, and is an area almost free of metallic artifact, this technique is applicable for use with conventional CT scanners with limited CT scale. In the second in-vitro validation study, a CT protocol was developed to use a multi-slice spiral CT scanner with an extended CT scale (up to 40,000 HU) for the measurement of acetabular periprosthetic bone defects. This technique enabled volumetric measurements of bone defects in all acetabular and periacetabular areas. In the third study, the clinical application of the developed CT technique was investigated in two sub-studies. The aim of the first clinical studywas to determine, using quantitative CT, the distribution, volume and rate of progression of PO lesions around 46 cementless THR prostheses in 33 patients. The findings showed that, in the long term, there were differences in the distribution of osteolytic lesions between different designs of cementless acetabular components. In particular, osteolysis commonly involved sites of access of the joint fluid- the peripheral region of the components, where prosthesis fixation is important, and fixation screw holes. The aim of the second clinical study was to use quantitative CT to determine the progression of osteolysis and the factors that may associate with it, including component migration, liner polyethylene wear, and patient variables, in 30 patients with 38 cementless acetabular components. The data provided the first reliable information on the progression of osteolytic lesions around uncemented THR prostheses and suggested that, for THR, the rate of polyethylene wear is a strong predictor of PO progression. The results from in-vitro studies and the findings from the clinical studies suggest that the use of this CT technique allows investigation of the natural history of osteolytic lesions, and will enhance preoperative planning, improve monitoring of THR patients, and enable measurement of the outcomes of new ways to manage PO.